Search All of the Math Forum:
Views expressed in these public forums are not endorsed by
Drexel University or The Math Forum.


dpb
Posts:
9,085
Registered:
6/7/07


Re: Multiplying Double and a Logical
Posted:
Jun 18, 2012 7:52 PM


On 6/18/2012 6:09 PM, Michael wrote: > Hello all. This is my first post and this may be a silly question, but I > googled the shit out of this to no avail... > > I have an array with some NaNs (which is a double), the array is also, > therefore, a double). I'd like to (pointwise.*) multiply this with > another array (equal dimension) that is a logical.
Well, a Matlab logical is also a double w/ the logical internal flag set so if you really want a pointbypoint multiply of conformant arrays, just do it...
>> d=1:3; >> l=logical([0 1 0]); >> whos d l Name Size Bytes Class
d 1x3 24 double array l 1x3 24 double array (logical)
>> p=d.*l p = 0 2 0 >> whos p Name Size Bytes Class
p 1x3 24 double array
>>
...
> Essentially I'm trying to plot something like [ 1 2 3 NaN] with [ 1 3 5 > 7] (as crude examples). When plotting I'd only get three points (exactly > as I want). But I'm making a 'cut' in the data by multiplying a logical > (the cutcomposed of 1's and 0's) and a double (the actual data > containing some NaNs). > > I appreciate any help you have!
I can't follow precisely the question...use of NaN to not display selected points in plot() and friends is a wellrespected technique but that seems to be ok if I get your drift.
If you want some other selection criterion as well, use of logical addressing is one way but you don't multiply, you use the logical subscript to select the points desired.
Try
x=[1 2 3 NaN]; y=[1 3 5 7]; l=logical(1 1 0 1); plot(x(l),y(l)
Is that the desired result?
Read section on 'Logical Subscripting" in the Getting Started online doc's.




